654STORMWATER TREATMENT PRACTICES

654

6-220SECTION 654 – STORMWATER TREATMENT PRACTICES

654.01DESCRIPTION . This work shall consist of constructing stormwater treatment practices as shown

on the Plans.

654.02MATERIALS . Materials shall meet the requirements of the following subsections:

Granular Borrow ................................ ................................ ................................ ........ 703.04 Fine Aggregate for Concrete ................................ ................................ ...................... 704.01 Coarse Aggregate for Concrete ................................ ................................ .................. 704.02 Gravel Filter for Slope Stabilization ................................ ................................ .......... 704.07 Drainage Aggregate ................................ ................................ ................................ ...704.16 Stone Fill ................................ ................................ ................................ .................... 706.04 Corrugated Polyethylene Pipe (CPEP) ................................ ................................ ......710.03 Acrylonitrile -Butadiene -Styrene (ABS) Plastic Pipe ................................ ................. 710.0 4 Polyvinyl Chloride (PVC) Plastic Pip e ................................ ................................ ......710.0 5 Bar Reinforcement ................................ ................................ ................................ .....713.01 Iron Castings ................................ ................................ ................................ .............. 715.01 Geotextile for Roadbed Separator ................................ ................................ .............. 720.02 Geotextile for Underdrain Trench Lining ................................ ................................ ..720.05 Compost ................................ ................................ ................................ ..................... 755.05 Geomembrane Liner ................................ ................................ ................................ ..760.07 Clay soil shall meet the requirements of Table 703.01A for group classific ation A-7-6. Precast concrete shall meet the requirements of Section 540 . Cast-in-place concrete shall meet the requirements of Section 541 for Concrete, Class B. Bedding for gravel wetland shall conform to the requirements of Subsection 704.02 . The layer of 1-1/2 inch bedding shall be in accordance with Table 704.02 D. The layer of 3/8 inch bedding shall be in accordance with Table 704.02 B. Media filter drain soil shall consist of mineral aggregate, perlite, dolomite lime, and gypsum in the quantities shown in the Vermont Stormwater Management Manual Rule and Design Guidance , Table 6 -

Vermont Stormwater Management Manual Rule and Design Guidance, Table 6 -1. The mineral aggregate component shall meet the requirements of Table 704.02 B. Bioretention soil shall meet the requirements of Table 654.0 2A.

654

6-221TABLE 654.02A – COMPOSITION OF BIORETENTION SOIL

Component Min. Max. Sand 85% 88% Silt 8% 12% Clay 0% 2% Organic matter in the form of compost 3% 5%

654.03GENERAL REQUIREMENTS . The stormwater treatment practices, and the areas draining to

them, shall be fully stabilized prior to allowing water to drain to them.

654.04DRY SWALE AND DRY SWALE WITH UNDERDRAIN . Dry swales shall be constructed at

the locations shown on the Plans. Geotextile fabric shall meet the material requirements of Subsection

720.05and placement shall be performed in accordance with Section 649 . Where required, underdrain

shall be installed in accordance with Section 605 . Dry swale soils shall consist of natural or manufactured sand meeting the requirements of Subsection

704.01

The Contractor shall not place dry swale soil directly from haul vehicles or by pushing material by bulldozers, graders, or other equipment.

654.05GRAVEL WETLAND . Gravel wetla nds shall be constructed at the locations shown on the Plans

Gravel wetlands shall be comprised of a network of underdrain pipes placed in a bedding of crushed stone and connected to an outlet structure, as shown on the Plans. Bedding for gravel wetlands shall consist of a layer of 3/8 inch bedding on top of a layer of 1 -1/2 inch bedding installed to the depths shown on the Plans. Unless otherwise specified, the bottom and sides of the gravel wetlands shall be lined with either a clay soil, at a depth spe cified in the Plans, or geomembrane liner, as shown on the Plans. Geotextile for roadbed separator shall then be placed over the impermeable liner before placing the stone bedding. Placement of geotextile fabric shall be performed in accordance with Secti on 649 and underdrain shall be installed in accordance Section 605 , except as modified herein.

654 6-222 654.06 SURFACE SAND FILTER . Surface sand filters shall be constructed at the locations shown on the Plans. Placement of geotextile fabric shall be performed in accordance with Section 649 . Where required, underdrain shall be installed in accordance with Section 605 . Surface sand filter soils shall consist of natural or manufactured sand meeting the requirements of Subsection 704.01 . The Contractor shall not place surface sand filter soil directly from haul vehicles or by pushing material by bulldozers, graders, or other equipment.

654.07UNDERGROUND SAND FILTER . This work shall consist of designing and installing an

underground precast or cast -in-place conc rete sand filter as detailed and at the locations shown on the Plans. Design drawings and calculations shall be submitted for review and approval in accordance with Subsection 105.06 . For precast concrete, fabrication drawings shall be submitted for review and approval in accordance with Subsection 105.06 . Unless otherwise specified in the Contract, the design live load for all concrete elements shall be H -20 in accordance with the AASHTO Standard Specifications for Highway Bridges . The underground sand fil ter media shall consist of natural or manufactured sand meeting the requirements of Subsection 704.01 .

654.08MEDIA FILTER DRAIN . Media filter drains shall be constructed at the locations shown on the

Plans. Placement of geotextile fabric shall be perfor med in accordance with Section 649 . Underdrain shall be installed in accordance with Section 605 . The Contractor shall not place media filter drain soil directly from haul vehicles or by pushing material by bulldozers, graders, or other equipment.

654.09BIORETENTION AREA . Bioretention areas shall be constructed at the locations shown on the

Plans. Geotextile shall be in accordance with Subsection 720.02 and placed in accordance with Section 649 .

654

6-223When the Plans require underdrain to be installed unde r the bioretention areas, the underdrain shall be

installed prior to the bioretention area and in accordance with the respective underdrain pay item. For bioretention areas where underdrain is installed under the area, the Contractor shall conduct an available phosphorus soil test on the bioretention soil media using the modified Morgan Method, or approved equivalent , to ensure that the media will not leach phosphorus. The available phosphorus for the soil must be less than 0.2% phosphorus. Test results dem onstrating compliance shall be obtained prior to placement of the bioretention soil media. The Contractor shall provide a record of the phosphorus test results to the Engineer for the Agency’s use in subsequent design certification requirements.

654.10STONE DIAPHRAGM. This work shall consist of furnishing and installing a stone trench for the

purpose of providing initial stormwater treatment and distributing flows at the locations indicated on the Plans and as directed by the Engineer. The stone diaphragm shall be comprised of a trench lined with geotextile meeting the requirements of Subsection 720.05 and filled with stone meeting the requirements of Subsection 704.16 . Trenches for stone diaphragms shall be excavated to the dimensions and grade shown in the Plans or as directed by the Engineer. The surface of the trench shall be prepared to a smooth condition free of debris, depressions, or obstructions which may damage the geotextile. The geotextile fabric lining the trench shall be placed loosely with no wrinkles or folds. The upstream geotextile shall be overlapped over the downstream. Care shall be taken to ensure direct contact with the soil such that there are no voids between the geotextile and the trench. The geotextil e lining shall be anchored by extending 12 inches beyond each side of the trench at a depth of 4 inches below finished grade. Drainage aggregate shall be placed in layers of not more than 6 inches in thickness and compacted by use of air or mechanical tam pers.

654.11METHOD OF MEASUREMENT . The quantity of Dry Swale, Dry Swale with Underdrain,

Media Filter Drain, and Stone Diaphragm to be measured for payment will be the number of linear feet installed in the complete and accepted work. The quantity of Un derground Sand Filter to be measured for payment will be the number of each installed in the complete and accepted work. The quantity of Gravel Wetland, Surface Sand Filter, and Bioretention Area to be measured for payment will be the square yards installe d in the complete and accepted work, measured based on the neat lines showing the finished surface area on the Plans.

654 6-224 654.12 BASIS OF PAYMENT . The accepted quantity of Dry Swale and Stone Diaphragm will be paid for at the Contract unit price per linear foot. Payment will be full compensation for furnishing, transporting, handling, and installing the materials specified, and for furnishing all labor, tools, equipment, and incidentals necessary to complete the work. The accepted quantity of Dry Swale with Underdrain and Media Filter Drain will be paid for at the Contract unit price per linear foot. Payment will be full compensation for furnishing, transporting, handling, and installing the materials specified including underdrain, geotextile, and for furni shing all labor, tools, equipment, and incidentals necessary to complete the work. The accepted quantity of Gravel Wetland will be paid for at the Contract unit price per square yard. Payment will be full compensation for furnishing, transporting, handling , and installing the materials specified including underdrain, impermeable liner, geotextile, and crushed stone bedding, and for furnishing all labor, tools, equipment, and incidentals necessary to complete the work. The outlet structure, inlet and outlet pipes will be paid for separately under their respective Contract items. The accepted quantity of Surface Sand Filter and Bioretention Area will be paid for at the Contract unit price per square yard. Payment will be full compensation for furnishing, trans porting, handling, and installing the materials specified including underdrain and geotextile, and for furnishing all labor, tools, equipment, and incidentals necessary to complete the work. Landscape plantings, if specified, will be paid for separately un der their respective Contract items. Underdrain placed under bioretention areas will be paid for separately under the appropriate Contract pay item. The accepted quantity of Underground Sand Filter will be paid for at the Contract unit price for each. Paym ent will be full compensation for designing, furnishing, fabricating, transporting, handling, and installing the materials specified, including, but not limited to, the trash rack, sand filter bedding, concrete

vault, concrete top slab with lift rings, bar reinforcement, manhole covers and steps, debris screen,

underdrain, geotextile, entrance grates, and drainage aggregate; any sheeting, bracing, dewatering and

siltation control; preparing and submitting working drawings; and for furnishing all labor, tools,

equipment, and incidentals necessary to complete the work. Catch basins, inlet and outlet pipes, and stone

fill outlet protection attached to the Underground Sand Filter will be paid for under their respective

Contract items.

For all stormwater treatment practices, excavation will be paid for under the appropriate excavation item

included in the Contract. Topsoil, turf establishment, and mulch will be paid under their respective

Contract items.

654

Payment will be made under:

Pay Item Pay Unit

654.0010 Dry Swale..................................................................................................Linear Foot

15 Dry Swale with Underdrain ......................................................................Linear Foot

20 Gravel Wetland .........................................................................................Square Yard

30 Surface Sand Filter ....................................................................................Square Yard

40 Underground Sand Filter...........................................................................Each

50 Media Filter Drain.....................................................................................Linear Foot

60 Bioretention Area ......................................................................................Square Yard

70 Stone Diaphragm ......................................................................................Linear Foot

655

6-226SECTION 655 – WILDLIFE HABITAT FEATURES

655.01DESCRIPTION . This work shall consist of providing and installing features for the protection,

preservation, restoration, or management of wildlife habitat.

655.02MATERIALS . Materials shall meet the requirements of the following subsections:

Miscellaneous Hardware, Shapes, and Fabricated Materials ................................ .....709.01(h) Nonstructural Lumber ................................ ................................ ................................ 709.02 Timber Preservative ................................ ................................ ................................ ...726.01 Woven Wire Fence ................................ ................................ ................................ ....727.01 Chain -link Fence ................................ ................................ ................................ ........ 727.02 Snow Barrier Fence ................................ ................................ ................................ ....727.05 Plank Rail Fence ................................ ................................ ................................ ........ 727.06 Sign Posts ................................ ................................ ................................ ................... 750.01 Boulders shall be natural river material. The middle dimension of any boulder shall not be less than 16 inches. The middle dimension of at least half the boulders placed shall be at least 24 inches. Suitable boulders excavated during construction may be used.

655.03STREAM HABITAT BOULDERS. This work shall consist of placing natural river boulders

throughout the finished stream channel. The Contractor shall notify the Engineer a minimum of 7 calendar days prior to placement of the boulders. Boulders shall be placed as directed by the En gineer at intervals defined in the Plans. Distribution of boulders shall be in a generally random fashion throughout the channel, except in locations to be identified by the Engineer at the time of construction, where boulders shall be either clustered or excluded. The largest boulders shall be used at the toe of the slope (bottom 2 to 3 vertical feet), with no chinking stone used on the front face so that gaps remain between stones to provide improved aquatic habitat.

655.04WILDLIFE GUIDE FENCES . This w ork shall consist of furnishing and installing wildlife guide

or exclusionary fences at the locations indicated on the Plans and as directed by the Engineer. Fences shall be constructed in conformance with the Plans and Section 620 .

655.05WILDLIFE SHELF . This work shall consist of constructing a shelf within a culvert or under a

bridge at the locations indicated in the Plans to facilitate animal passage. The shelf shall be constructed in conformance with the Plans and as directed by the Engineer.